Conventionally, printing presses have been used as a means to quickly produce massive amounts of printed materials. However, in the printing industry, there are a significantly large number of orders for small printing jobs which are unprofitable if the printing plate is made. Therefore, so-called on-demand printing, which is a print making technique suitable for executing such a small amount of printing, has been required.
As an image forming technique which is capable of quickly and inexpensively making a small number of printed materials, an electrophotographic image forming technique is attracting attention. The electrophotography includes two types of methods: a dry-process image forming method and a wet-process image forming method. The wet-process image forming method can produce toner images of excellent quality.
The wet-process image forming method uses a liquid developer in which toner is dispersed into an insulating liquid; and from perspectives of the fast image forming process and the compact developing equipment, high-density liquid developers are used which contain a high concentration of toner. However, the use of a high-density liquid developer tends to create uneven thickness of the film when a thin layer of liquid developer is formed on the development roller. As a result, there is a problem in that uneven density occurs on the image. Also, toner gets on the non-image portion on the image carrier, causing toner fog on the white background, which has been a problem.
Accordingly, a technique has been studied which uses a high-density liquid developer to form a thin layer on the development roller. Specifically, a method (for example, see patent document 1) has been proposed in which a stirring member incorporated into the liquid developer storage tank stirs the developer in the storage tank of the development apparatus, thereby decreasing the developer's viscosity, and then the low-viscosity liquid developer is applied onto the development roller.
Furthermore, a liquid development apparatus (for example, see patent document 2) has been proposed which is equipped with a slit-type discharge outlet positioned along the direction of the development roller's axis so that the supply rate of liquid developer in the axial direction of the development roller is constant, and the apparatus is also equipped with a liquid developer supply head that has fewer components than the conventional apparatus, which makes the apparatus inexpensive and compact.
[Patent document 1] Japanese Laid-Open Patent Application No. 2001-194913
[Patent document 2] Japanese Laid-Open Patent Application No. H9-258520
However, a liquid development apparatus disclosed in patent document 1 has more components than the conventional apparatus due to a stirring device for stirring the liquid developer contained in the liquid developer storage tank. Furthermore, a large, high-torque drive motor is used for the stirring operation. Consequently, costs and the size of the development apparatus have been increased, which makes it impossible to provide a compact image forming apparatus.
On the other hand, if a high-density liquid developer is used in a liquid development apparatus disclosed in patent document 2, air is mixed into the liquid developer between the liquid developer supply head's discharge outlet and the development roller due to the developer's high viscosity, causing the discharge rate of the liquid developer from the discharge outlet to intermittently increase and decrease, thereby making it impossible to steadily apply the developer onto the development roller. As a result, it is impossible to form a uniformly thin layer of the liquid developer on the development roller, thereby failing to eliminate the occurrences of uneven density and toner fog.
An object of the present invention is to provide a liquid development apparatus, a liquid development method and an image forming apparatus which are capable of forming a uniformly thin layer of liquid developer on the development roller while using a highly viscous liquid developer which contains a highly dense toner.
In view of forgoing, one embodiment according to one aspect of the present invention is a liquid development apparatus, comprising:
an image carrier on which an electric latent image is formed;
a development roller which is arranged in an opposing position to the image carrier and develops the electric latent image with a thin layer of liquid developer, provided on a surface of the development roller, containing toner and charier liquid;
a storage tank which stores the liquid developer;
a liquid developer supply head which includes a discharge outlet which is provided in a direction of an axis of the development roller and discharges the liquid developer from the storage tank on the surface of the development roller; and
a viscosity reducing member which is provided in a vicinity of the discharge outlet.
According to another aspect of the present invention, another embodiment is a liquid development method, comprising the steps of:
reducing a viscosity of liquid developer in a liquid developer supply head which includes a discharge outlet which is provided in a direction of an axis of a development roller and discharges the liquid developer from the storage tank on the surface of the development roller;
forming a thin layer of the liquid developer by discharging the liquid developer from the discharge outlet; and
developing an electric latent image formed on a image carrier with the thin layer of the liquid developer;
wherein a member which reduces a viscosity of the liquid developer and is provided in a vicinity of the discharge outlet.
According to another aspect of the present invention, another embodiment is an image forming apparatus, comprising;
a storage tank which stores liquid developer containing toner and carrier liquid;
a liquid developer supply head which includes a discharge outlet for discharging the liquid developer from the storage tank; a development roller which carries a thin layer of the liquid developer discharged from the discharge outlet;                an image carrier on which an electric latent image is formed; anda member which reduces a viscosity of the liquid developer and is provided in a vicinity of the discharge outlet of the liquid developer supply head;wherein the electric latent image is developed by transferring the thin layer of the liquid developer to the electric latent image by the development roller.        